LZTS2 Regulation by PKCK2 modulates Wnt signaling

Abstract

Protein kinase casein kinase 2 (PKCK2) is a constitutively active serine/threonine kinase overexpressed in many types of human cancer. PKCK2 is a positive regulator in Wnt signaling pathway, since it stabilizes ?-catenin, thereby increasing its nuclear translocation, binding to Tcf/Lef (T-cell factor/lymphoid enhancing factor) components and activating the transcription of Wnt target genes.Leucine zipper putative tumor suppressor 2 (LZTS2) is frequently lost in a variety of human tumors. The LZTS2 interacts with ?-catenin and represses ?-catenin mediated transcription on TCF/LEF, however, little is known about PKCK2 mediated regulation of LZTS2.This study presented the identification of LZTS as a novel binding protein to PKCK2, the role of PKCK2-mediated phosphorylation on LZTS2, and its effect on Wnt signaling. The interaction between LZTS2 and PKCK2 was initially identified by a yeast two-hybrid screening and was further confirmed by GST pull down and co-immunoprecipitation. Mutational analysis and in vitro kinase assay indicate that LZTS2 contains multiple PKCK2 phosphorylation sites. In addition, it is demonstrated that PKCK2 stabilizes LZTS2 by phosphorylation in a proteasome dependent manner. Moreover, PKCK2 inhibition by TBB, a PKCK2 inhibitor, induced an accumulation of LZTS2 in the nucleus which further blocked the translocation of β-catenin from the nucleus to the cytoplasm. Further, PKCK2 activityis required for the regulation of LZTS2-mediated TCF/LEF transcriptional program.Taken together, PKCK2 regulates the LZTS2 stability, and affects the subcellular localization of LZTS2 through its phosphorylation, thereby modulates ?-catenin mediated transcriptional activity in Wnt signaling.